Sanofi-Aventis’ share price took a slight dip on the news that the US Food and Drug Administration has only issued an approvable letter for Ambien CR, the controlled-released version of its blockbuster insomnia drug Ambien (zolpidem), which is also sold as Stilnox.

Sanofi said the information requested by the FDA is not related to the drug’s safety or effectiveness and added that it is working closely with the agency to address issues outlined in the letter, however a delayed launch is now inevitable.

The company was expected to be selling Ambien CR in the USA by mid-2005 but that could now be put back by as much as six months. The problem with any delay is that Ambien is set to lose patent protection in October 2006 – or 2007 if it wins an extension for paediatric use – so the time that Sanofi will have to switch patients over to the new version will be reduced ahead of generic competition.

Furthermore, Ambien, which is a vital drug for Sanofi with sales last year of $1.8 billion and comfortably the best-selling insomnia drug in the USA, faces yet more competition in that market from Sepracro’s recently launched offering, Lunesta (eszopiclone) [[08/04/05f]].